The present invention relates specifically to problems in the control of printing arrangements capable of operation in both one-side and two-side printing modes.
More specifically, the invention relates to problems in the control of printing arrangement of the aforementioned kind wherein changing back and forth between the one-side and two-side printing modes involves an alteration in the path of the travel of a sheet to be printed through the printing arrangement with a concomitant change in the length of such path. By way of example, in some printing arrangements, two printing stations are provided, each adapted during operation to print a different image. In the one-side printing mode, a sheet is transported through the printing arrangement along a predetermined path past the first printing station and is printed upon a first side thereof, and is then transported past the second printing station and printed again upon the same side thereof, for example so as to form a two-color image. In the two-side printing mode, the sheet is transported past and printed at the first printing station in the manner just mentioned; however, before the sheet reaches the second printing station it is flipped over or in some other manner detoured in such a way that upon arrival at the second printing station the hither to unprinted side of the sheet will be presented to the printing station and the hitherto unprinted side of the sheet will be printed, so that after passing both printing stations both sides of the sheet will have been printed. Usually, with such two-mode printing arrangements, it is desired to control the operation of various printing devices in the printing arrangement, such as offset rollers, dampening arrangements, etc., in a manner synchronized with the transport of the sheet to be printed through the printing arrangement. However, this kind of synchronization is made difficult by the presence of two operating modes, inasmuch as changeovers back and forth between the two operating modes involve alterations in one or more portions of the path of travel of the sheet with a concomitant change in the overall length of such path of travel. The result is a loss of correlation between specific portions of the path of travel and any timing or sequencing control circuitry associated with printing devices to be actuated when the sheet reaches certain specific portions of the path of travel.